A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core plate and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds the both the core plate and the top guide. The top guide includes several openings, and fuel bundles are inserted through the openings and are supported by the core plate.
A plurality of openings are formed in the bottom head so that components, such as in core monitor assemblies and control rod drive assemblies, can extend within the RPV. Typically, a substantially cylindrical stub tube, or guide tube, having a bore extending therethrough is welded to the bottom head and the tube bore aligns with an opening in the bottom head. The cylindrical stub tube typically is fabricated from a corrosion resistant material such as stainless steel or Ni--Cr--Fe.
With an in core monitor assembly, for example, the in core monitor housing, e.g., a tube, is inserted through the bottom head opening and stub tube bore, and the housing extends into the RPV. The in core monitor housing (ICMH) is welded to the stub tube to maintain the housing in the desired position. The stub tube thus serves as a transition piece between the bottom head dome, which typically is fabricated from low alloy steel, and the CRD housing, which typically is fabricated from stainless steel.
When performing maintenance or repairs in an RPV, it often is desirable to acquire electrochemical corrosion potential (ECP) measurements for RPV components such as pipes and in core monitor housings. To obtain ECP measurements for an in core monitor housing, for example, it is desirable to machine an opening in the in core monitor housing (ICMH) sidewall. One known method of machining an opening in the ICMH requires positioning a machining tool, i.e., an electrical discharge machine, adjacent an exterior surface of the sidewall, and activating the apparatus to machine an opening through the ICMH sidewall. This approach, however, is time consuming and often impractical. Particularly, depending on the size and location of the ICMH or pipe to be machined, it often is difficult to position the tool adjacent the exterior surface of the ICMH or pipe.
Accordingly, it would be desirable to provide an apparatus for machining pipes and valves in a nuclear reactor more easily than by known methods. It also would be desirable to provide such an apparatus which is inexpensive and easy to operate.